The sulfuric acid method and enzymatic methods are examples of conventional cellulose hydrolysis methods. However, the sulfuric acid method presents problems such as corrosion of the reactor and processing to neutralize reaction waste products. Enzymatic methods present problems in that the enzymes are expensive and of low activity, and in that the enzymes must be separated from the reaction product. There is also the method of hydrolyzing cellulose in subcritical or supercritical water at 300° C. and above. For example, a report by Arai et al. of Tohoku University (Nonpatent Reference 1) states that a large variety of products are produced and glucose selectivity is not high.
The pressurized hot water method employing a solid catalyst is an example of a substitute method for the above. The pressurized hot water method affords an advantage in that neutralization processing and separation processing are not required. However, it requires the development of catalysts with activity that can withstand the conditions of pressurized hot water.
In recent years, Hara et al. of the Tokyo Institute of Technology (Nonpatent Reference 2) and Onda et al. of Kochi University (Nonpatent Reference 3) have reported cellulose hydrolysis reactions employing solid acid catalysts comprised of carbon on which sulfuric acid was immobilized. These reports claimed that oligosaccharides or glucose was obtained as the main reaction product. It also stated that glucose, in particular, was an important compound because it could be converted to bioplastics and biofuels.
Patent Reference 1 discloses a liquefying method of cellulose-based biomass comprising the steps of reacting a cellulose-based biomass starting material with functional groups on a carrier surface and conducting hydrothermal decomposition. The examples of inorganic solids such as activated carbon are given for the carrier. Patent Reference 2 discloses a method of hydrolyzing cellulose comprising the step of heating a reaction solution comprised of a solid catalyst having an acidic or a basic functional group within the molecule, dispersion water, and a cellulose starting material. Activated carbon is given as an example of the solid catalyst.    Patent Reference 1: Japanese Unexamined Patent Publication (KOKAI) 2009-296919    Patent Reference 2: Japanese Unexamined Patent Publication (KOKAI) No. 2006-129735    Patent Reference 3: WO2010/067593    Nonpatent Reference 1: Ind. Eng. Chem. Res., 39, 2883-2990 (2000)    Nonpatent Reference 2: J. Am. Chem. Soc., 130, 12787-12793 (2008)    Nonpatent Reference 3: Green Chem., 10, 1033-1037 (2008)    Nonpatent Reference 4: J. Phys. Chem. B, 103, 7743-7746 (1999)
The entire contents of Patent References 1 to 3 and Nonpatent References 1 to 4 are hereby incorporated by reference herein.